Page 131 - MNU-PM502- Pharmaeutical Microbiology Theoritical Book

Pharm D- Clinical Pharmacy Program Third Level Pharmaceutical Microbiology& Antimicrobials (PM 502)

Mechanism of resistance to common antimicrobial agents

1- Beta-lactam

a- Enzymatic inactivation (beta-lactamases)

b- Altered penicillin - binding proteins (methicillin – resistant Staphylococcus
aureus

2- Non Beta-lactam antibiotics

A- Vancomycin: Alter target of drug so it can not bind to the new target

B- Bacitracin: Increased synthesis of the bactoprenol molecule

3- Polymyxins

• The loss of outer membrane porin proteins,
• A reduction in binding of polymyxin to the cell envelope as a result of

changes in lipid and LPS composition.
4- Aminoglycosides

• Production of aminoglycoside inactivating enzyme that chemically modifies
drug (the most common mechanism).
• Reduced uptake or decreased cell permeability

• Altered ribosome binding Sites
5- Tetracyclines: Cells become resistant to tetracycline by at least three

mechanisms:
• Enzymatic: Inactivation is the rarest type of resistance, where an acetyl
group is added to the molecule, causing inactivation of the drug.

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